wNew equipment play in this service. In their experience, approximately one third of all equipment losses are electrical in nature and about one quarter of these losses are caused by loose connections. On average, about eight electrical problems or hot spots are detected on each survey, and of these, four are minor or intermediate, and four are serious or critical - based on their temperature rise above normal or above that of related objects. The Thermovision 480 will be used in applications where single unit imagers are not as suitable. Because the THV480 has a separate control unit and scanner, it can be used to inspect confined spaces which would normally prohibit the use of one larger combined unit. A top mounted LCD screen on the control unit also enables colour images to be viewed at a glance out in the field.
AGEMA Infrared Systems, Arden House, West Street, Leighton Buzzard, Bedfordshire LU7 7DD, UK
Improved ultrasonic transducers Advances in materials, the growth of quality and safety requirements and the demand for faster inspection speeds are forcing industry to seek more effective and powerful inspection systems. This is particularly true in high technology areas such as aerospace and nuclear energy.
A rangeof the piezo-compositeultrasonictransducersdevelopedby Sodern and Philips ElectronicsLaboratories damped, with large bandwidth and high sensitivity, which provides high axial resolution, reduced dead zone and good contrast. The use of composite materials enables the transmitting surface of the transducer to be easily formed to the required shape. This avoids the need for acoustic lenses which attenuate the ultrasonic signal. Thorough testing of a sample often requires the use of more than one sensor. One solution is to group a number of sensors into an array and to carry out focusing and beam steering electronically. Simple arrays can be annular or linear, and complex arrays can be manufactured to give improved resolution and inspection speeds.
To help meet this demand, the French company Sodern and Philips Electronics Laboratories have combined their medical ultrasonics expertise to develop a range of ultrasonic transducers and inspection systems for N DT.
Signal processing is carried out on the transducer outputs to improve resolution by the use of dynamic focusing, for example, or to reduce the noise produced with certain 'multidiffuser' materials and to display the output so that defects in the sample are easy to identify.
The new sensors are made from a piezo-composite material. They are highly
Sodem, 20 avenue Descartes, 94451, LimeiI-Brevannes C~dex, France
NDT& E International Volume 25 Number 3 1992
Stress analysis for air crash investigations Investigation of the mechanical stresses which caused a repaired pressure bulkhead to fracture, leading to the JAL disaster in 1985, has resulted in a call to establish retirement conditions for ageing aircraft. The call was made by the National Aerospace Laboratory (NAL) in Tokyo, who have carried out extensive research to discover why the bulkhead failed and what countermeasures could be taken to maintain structural integrity. NAL has undertaken experimental work to simulate service Ioadings and has investigated the mechanical stresses introduced by using a full field measurement technique pioneered in the UK by Ometron Ltd. This technique permits non-contacting measurement of mechanical stress by making use of the thermoelastic principle. In so doing a pictorial image of stress distributions across large sections, such as aircraft